After completing this article, the reader should be able to:
* Identify the basic anatomy seen on a chest radiograph.
* Describe the anatomical relationships of various organs in the
chest.
* Describe the basic positioning requirements for a chest exam.
* List the criteria used to critique a chest radiograph. * Identify
radiologists' requirements for interpreting a chest radiograph.
* Discuss several common disease processes of the lungs and their
radiographic appearances.
* Evaluate a chest radiograph for various devices such as
endotracheal tubes, chest tubes and central venous catheters.
* Describe several pathologies of the chest.
Chest radiography is the most common radiographic procedure
performed in medical imaging departments, and one of the most often
repeated exams. (1-3) It is estimated that in the United States 68
million chest radiographs are performed each year. (4) Chest radiography
is performed to evaluate the lungs, heart and thoracic viscera.
Additionally, disease processes such as pneumonia, heart failure,
pleurisy and lung cancer are common indications. The American College of
Radiology (ACR) and others suggest that daily chest radiographs are
indicated for critically ill patients. (5-7) This includes patients on
ventilators, as well as those with acute cardiopulmonary problems.
According to the ACR Practice Guidelines for the Performance of
Pediatric and Adult Chest Radiography, there are several indications for
a chest radiograph. (5) Some of these indications include:
* Evaluation of signs and symptoms potentially related to the
respiratory, cardiovascular and upper gastrointestinal systems, as well
as the musculoskeletal system of the thorax. The chest radiograph also
can help to evaluate thoracic disease processes, including systemic and
extrathoracic diseases that secondarily involve the chest. Because the
lungs are a frequent site of metastases, chest radiography can be useful
in staging extrathoracic, as well as thoracic, neoplasms.
* Follow-up of known thoracic disease processes to assess
improvement, resolution or progression.
* Monitoring of patients with life-support devices and patients who
have undergone cardiac or thoracic surgery or other interventional
procedures.
* Compliance with government regulations that mandate chest
radiography. Examples include surveillance posteroanterior chest
radiographs for active tuberculosis or occupational lung disease or
exposures and other surveillance studies required by public health law.
* Preoperative radiographic evaluation when cardiac or respiratory
symptoms are present or when there is significant potential for thoracic
pathology that could compromise the surgical result or lead to increased
perioperative morbidity or mortality. (5)
The radiographer's role is to provide the physician with an
image of the chest that is diagnostic and aids in the treatment of the
patient. This cannot be accomplished satisfactorily without adequate
knowledge of chest anatomy, pathology and consistent positioning in both
the ambulatory and bedridden patient.
Normal Chest Anatomy
The Bony Thorax
The bony thorax of the chest is composed of the sternum anteriorly
and 12 pairs of ribs that surround the lungs. Each pair of ribs connects
to a corresponding thoracic vertebra posteriorly. The posterior rib
attachments connect at the costovertebral and costotransverse joints.
Each rib wraps around the lung and descends approximately 3 to 5 inches
from its highest point posteriorly. (2) (See Figure 1.) The anterior
portion of each rib connects by way of costocartilage to the sternum.
The costocartilage usually does not show up on a radiograph unless it is
calcified. The true ribs, numbers 1 though 7, connect anteriorly to the
sternum by way of this costocartilage. (See Figure 2) The false ribs are
numbers 8 through 12. Ribs 8 through 10 connect to the sternum by way of
the costocartilages of the seventh ribs. False ribs 11 and 12 are short
and do not wrap around the body; they also are called floating ribs. The
ribs collectively provide a protective framework for the lungs.
[FIGURES 1-2 OMITTED]
The Respiratory System
The respiratory system is composed of the larynx, trachea, bronchi
and lungs. The larynx, commonly referred to as the voice box, is the
most superior structure in the respiratory system and houses the vocal
cords. In close proximity to the larynx are the thyroid cartilage,
laryngeal prominence or Adam's apple, and the cricoid cartilage.
The epiglottis also is located nearby and acts as a covering for the
trachea when food is swallowed. The trachea descends inferiorly
beginning at about the level of C5 to approximately T5 or T6, where it
bifurcates at the carina into the right and left primary bronchi. The
bronchi then subdivide into several branches. Three secondary branches
feed the right lung and 2 secondary branches feed the left lung. These
branches divide into tertiary levels and smaller segments, eventually
ending in the terminal bronchioles where the alveoli exchange oxygen and
carbon dioxide. (2)
The Lungs
The lungs are composed of a spongy material called the parenchyma.
The parenchymal tissue contains the fine structures of the bronchial
trees and pulmonary circulation. The exchange of oxygen and carbon
dioxide takes place at the alveolar level within the parenchyma. There
are millions of alveolar sacs within each lung. Daniels and Orgeig
stated that "in humans there are ~25 branches and 300 million
alveoli. This structure allows for the generation of an enormous
respiratory surface area (up to 70 m2 in adult humans)." (8)
The alveoli are composed of 2 types of cells, identified as Type I
and Type II cells. Daniels and Orgeig defined the purpose of each of
these cell types as follows:
* Type I cells are the main constituent of the walls of each
alveolus.
* Type II cells secrete surfactant, (8) which reduces surface
tension, thus reducing the tendency of the alveolar sacs to collapse.
(9)
The pulmonary arteries and veins supply blood to all portions of
the lungs. This network surrounds the alveoli, where oxygen and carbon
dioxide are exchanged with the blood. (2) (See Figure 3.)
[FIGURE 3 OMITTED]
Divisions of the Lungs
Structurally, the right lung is composed of 3 lobes. They are named
according to location as the upper, middle and lower lobes. The upper
and middle lobes are separated by a fissure called the horizontal
fissure. Occasionally, this fissure shows as a lucent line on a
radiograph. An additional oblique fissure separates the middle and lower
lobes.
The left lung is composed of 2 lobes--a superior and inferior lobe
divided by an oblique fissure. The lung parenchyma superior to each
clavicle is called the apical portion of the lung. This area is often
the hiding place for pulmonary nodules and can be hard to evaluate
because of the overlying anatomy of the clavicles. Radiographers use the
lordotic position to visualize this area.
Inferiorly, the lateral lung angles are in close proximity to the
ribs. These angles are named after their location: hence the term
costophrenic angles. (See Figure 4.) The right and left costophrenic
angles are important radiographically because they can be used to detect
effusions and other abnormalities. When this happens, they appear
flattened or blunted as a result of fluid buildup or retention.
[FIGURE 4 OMITTED]
Diaphragm
The diaphragm is a muscular structure located immediately below the
lung bases. Though it is a single organ, it is divided into 2 sections
called the right and left hemidiaphragms. The right hemidiaphragm is
higher on a chest radiograph because of the location of the liver, which
is immediately inferior to it. The term cardiophrenic angles is
sometimes used to describe the area where the heart's border comes
in contact with the diaphragm. There are both right and left
cardiophrenic angles, which should be visualized on a normal chest
radiograph. (See Figure 4.)
Pleura
Each lung is surrounded by a thin-walled sac called the pleura. The
pleura completely encases the lung with an inner layer called the
pulmonary or visceral layer and an outer layer called the parietal
layer. The potential space between these 2 layers is called the pleural
space. Radiographically, this space is important because it can fill
with air (pneumothorax) or blood (hemothorax), which can be seen on a
chest radiograph. A chest tube can be placed within the pleural space to
drain accumulated fluid or air.
The Mediastinum
The mediastium is the space between the lungs that houses the heart
and great vessels, including the proximal pulmonary arteries and aortic
root. Additionally, the proximal bronchial trees, pulmonary veins, a
portion of the esophagus and lymphatic vessels are important structures
found in the mediastinum. The hilum "is the central area of each
lung, where the bronchi, blood vessels, lymph vessels and nerves enter
and leave the lungs." (2) (See Figure 4.) Furthermore, the thymus
gland is located above the heart in the superior mediastinal
compartment.
Patient Preparation for the Chest Exam
All Patients
Prior to proceeding with the exam, all women of child-bearing age
should be asked if there is any possibility of pregnancy. The ACR
guidelines (5) suggest that all imaging facilities should have policies
and procedures in place that identify patients who might be pregnant
prior to exposing them with ionizing radiation. Additionally, clothing
that interferes with the exam should be removed. This includes items
such as bras,jewelry, buttons or any metal objects that could interfere
with the study. (5) T-shirts with prominent logos also should be removed
because they can show up on the study and can interfere with the
diagnosis. Long hair that is in braids or tightly held together with
rubber bands should be moved from the upper lung fields. (2) Figure 5
shows several artifacts that resulted in repeat radiographs.
[FIGURE 5 OMITTED]
Body piercings and especially nipple piercings are common metallic
foreign bodies that can interfere with interpretation and diagnosis.
This can be a delicate and embarrassing subject for patients. The
question should be phrased sensitively to avoid offending the patient.
It is not appropriate to ask a patient if he or she has a nipple
piercing. However, simply inquiring if all metal has been removed from
the chest area is appropriate. Some body piercings have been welded
closed and cannot be removed unless cut. Likewise, some patients will
not remove a body piercing because piercings can be difficult or
impossible to reinsert. In fact, the Association of Professional
Piercers on its Web site stated, "Even momentary removal of jewelry
from a healing piercing can result in amazingly rapid Closure of the
piercing and make reinsertion difficult or impossible." (10) This
site also claimed that metal piercings will not interfere with or
obstruct the visibility of pathology on a thoracic radiograph. The
decision to remove a piercing should rest with the patient. However, the
radiographer should explain that the patient might be asked to remove
the piercing on subsequent radiographs if it does indeed interfere with
a diagnosis. The choice to do this would still rest with the patient.
Inpatients and Portable Exam Preparation
Part of preparing a patient for the exam includes removing
irrelevant material from the area of interest. Radiographers performing
inpatient chest exams in the radiology department and portable chest
exams throughout the hospital should be particularly aware of this.
Extra time should be taken to ensure that external tubes and lines are
redirected from the imaging area. Inpatient gowns frequently contain
snaps that can interfere with the study. Sometimes these gowns can be
removed and replaced with snapless gowns. If not, the snaps should be
repositioned away from the field of view. Likewise, oxygen tubing,
electrocardiogram (ECG) leads, the external portions of nasogastric
tubes, enteral feeding tubes, temporary pacemakers and telemetry devices
should be directed to an appropriate area outside of the collimated
field. Care should be taken to avoid disconnecting or inadvertently
extracting these devices. Figure 6 demonstrates how distracting they can
be if not removed from the field of view. Time should be taken to move
these items because they interfere with the visibility of pertinent
anatomy. When they remain in the field of view they diminish the quality
of the exam, resulting in poor patient care and sometimes missed
diagnoses.
[FIGURE 6 OMITTED]
Radiography of the Chest
Conventional radiography of the chest has been described in several
positioning textbooks. (2,11) The basic radiographs include a
posteroanterior (PA) projection and lateral position. For acutely ill
patients, an anteroposterior projection (AP) often is obtained. If the
patient is in the emergency room (ER) or intensive care unit (ICU), AP
portable chest radiography usually is performed. It is interesting to
note that it has been estimated that in many medical centers up to 50%
of chest radiographs are performed with a portable x-ray machine. (12)
AP projections obtained with portable units have several disadvantages
compared with PA projections. These include magnification of the heart
and thoracic viscera, inability to obtain adequate inspiration because
of difficulty obtaining the study erect and technique variations caused
by inadequate placement of grids and screens.
Several authors have suggested that chest radiography should be
performed with a 72-inch source-to-image-receptor distance (SID) to
reduce magnification of the heart. (2,11) Some medical centers use a
120-inch SID for this reason. Quite often, an erect view is difficult to
obtain when performing chest radiography because of the patient's
condition. However, erect studies are preferred because they better
demonstrate pleural effusions and pulmonary edema. Furthermore, when the
patient is in an erect position the abdominal structures descend,
allowing the patient to take in a deeper breath. This results in a
better radiograph, with the lung parenchyma better visualized.
The PA Projection
The PA is performed by positioning the patient against the upright
Bucky. (See Figure 7.) First, adequate radiation protection should be
provided to the patient whenever possible. This means that the
radiographer should provide a wraparound apron or other shielding
devices as deemed appropriate. Next, the patient should stand in a
relaxed position facing the Bucky with the shoulders rolled forward.
Rolling the shoulders forward is important because it moves the scapular
bodies from the lung fields, allowing for better visualization of
parenchymal anatomy. The head should be extended slightly to avoid
cranial anatomy overlying the apical portion of the lungs. The placement
of the cassette should be about 2 inches above the patient's
shoulders. When using older film-screen technology this allows for
placement of the patient identification (ID) block outside of the lung
anatomy. With newer computed radiography (CR) equipment, placement of
the ID block is of less concern because it is not used for ID purposes.
With CR equipment this block is used to orient the image as it is being
read by the CR reader. Proper placement will result in an image display
on the computer monitor that is correctly oriented. Neither of these
issues are a concern with a direct radiography (DR) system because
cassettes have been replaced with permanent imaging plates. Regardless
of whether older analog systems or newer digital technology is used,
Bucky height is critical to preclude clipping anatomy; thus, adequate
placement is about 2 inches above the shoulders.
[FIGURE 7 OMITTED]
Bontrager (2) described an interesting method of positioning for
the PA chest exam, known as the hand-spread method. He recommended that
prior to using this method the radiographer should measure his or her
own thumb-to-little-finger distance. Sometimes it is also beneficial to
measure the distance between the index finger and thumb. Once these
distances are known, the measurements can be used to align the
patient's midlung field with the center of the imaging receptor
(IR). To accomplish this, the radiographer places the tip of his or her
small finger on the vertebra prominens (C7) while extending the thumb
inferiorly along the spinous processes. (See Figure 7, upper left
image.) Likewise, the index finger and the thumb also could be used. The
middle of the chest correlates to T7, which is located 7 inches inferior
to the vertebra prominens for most women and 8 inches inferior for most
men. The central ray is then placed at this level. This distance can
vary slightly depending on variations in body habitus, but it generally
holds true for most patients. For example, Bontrager (2) noted that
well-developed athletes with a sthenic or hyposthenic body habitus often
require centering between 8 and 9 inches from the vertebra prominens.
Conversely, a patient with a hypersthenic body habitus should be
centered between 6 and 7 inches from the vertebra prominens.
Next, the top of the collimated light field is put at the level of
the vertebra prominens. This corresponds to the level of the pulmonary
apices. Because of the divergent nature of the x-ray beam, when the
upper collimated beam reaches the IR all of the apices will be included
on the radiograph, thus precluding clipping important thoracic anatomy.
Likewise, by using this method the collimation at the bottom of the
radiograph includes the lung bases, thus providing equal collimation at
the top and bottom of the IR. This is an interesting method and with
practice can result in better-centered radiographs of the chest.
The exposure is made with high kVp, high mA and short exposure
time. The patient should be instructed to hold his or her breath on the
second inspiration. This allows for a better inspiratory effort and, as
a consequence, a radiograph with fully inflated lungs.
The Lateral Position
The lateral radiograph of the chest is performed by placing the
left hemithorax against the IR. The arms should be raised above the
head. Occasionally, an intravenous (IV) pole or other support can be
used to help maintain this position. The left lateral position is
routine because it places the heart closer to the IR.
The shoulder is in close contact with the IR superiorly; however,
depending on body habitus, this often results in greater object-film
distance inferiorly. This can be as much as 2 or 3 inches. Care should
be taken to ensure that the patient is standing straight and that the
body does not tilt toward the IR. It is tempting for new radiographers
to tilt the patient to reduce the object-film distance. However, this is
incorrect and should be avoided because the radiograph will appear
distorted. Tilt "may be evident by closed disk spaces of thoracic
vertebrae" on the radiograph. (2)
To ensure that the patient is standing in a true lateral position,
some radiographers place a hand on the patient's lower back, where
the ribs are easy to palpate. The radiographer can ensure
superimposition of the right and left rib cages by rotating the patient
if necessary while feeling the posterior ribs. When the
radiographer's hand is perpendicular to the IR, unwanted rotation
generally is eliminated. (See Figure 7, lower right image.) Again, the
exposure is made with high kVp, high mA and short exposure time. As in
the PA projection, the exposure is made upon the second inspiration.
The Portable AP
The portable exam is performed whenever the patient cannot come to
the department for traditional PA and lateral radiographs of the chest.
Sometimes a portable chest radiograph can be performed only with the
patient in the supine position. Whenever possible, however, it should be
performed with the patient erect or erect "to the greatest angle
tolerated by the patient." (11) Patients who are on ventilators or
have had recent surgery present a challenge when trying to position for
the AP, and the examination often must be performed with the patient
supine. As stated previously, care should be taken to reposition ECG
wires and tubes overlying the chest that interfere with physician
interpretation. Radiographers always should keep this in mind because
portable studies are performed on critical patients who present with all
sorts of paraphernalia.
Semierect films often appear lordotic when performed with the
portable x-ray machine. This happens when the x-ray tube and IR are not
properly aligned. The x-ray tube should be perpendicular to the IR to
avoid a lordotic appearance. However, if fluid levels are a concern, the
x-ray tube should remain in a horizontal position. In this scenario, to
avoid a lordotic appearance, a decubitus position should be considered.
These decisions are made by the radiographer and are paramount in
providing good patient care. This means that the radiographer should
evaluate the reason for the chest radiograph and then determine the best
method to use. For example, if the exam was ordered to demonstrate
possible pleural effusions, it should be performed with the patient
fully erect with a horizontal beam. If the patient's condition does
not allow for an erect examination, a lateral decubitus projection
provides similar information. On the other hand, if the portable exam is
ordered to demonstrate a line placement and the patient presents in a
semierect position, the x-ray tube should be tilted caudally to avoid a
lordotic appearance. This generally places the x-ray tube at a 90o angle
to the IR. Other factors such as the placement of grids and screens
require additional forethought on the radiographer's part.
Consistency in Positioning
It is not unusual for patients in the ICU to have portable chest
radiography performed daily. In these scenarios, similar positions
should be employed each day. This means that radiographers making these
exposures should check previous radiographs to ensure they are providing
uniformity in positioning and technique. Subtle changes often are noted
on daily radiographs when they are compared with each other. Such
findings could prompt changes in patients' medical treatment,
(7,13) as a study performed by Marik and Janower confirmed. (14) They
found that 66% of intubated patients and 25% of nonintubated patients in
an ICU had modifications in treatment based on results of daily chest
radiographs.
As a result, it is important that radiographers provide consistency
when performing chest radiography. Subtle changes seen on chest
radiographs should be the direct result of the patient's condition
and not a result of variations in positioning. Consistent positioning
can be accomplished only by providing adequate documentation on the
radiograph. To do this, some radiology departments use a sticker to
record this information. Newer digital technologies provide a way to add
electronic annotations to images. At a minimum, the sticker or
annotation should include the date and time of the exam, the distance
used, the patient's position and the technique employed. This
permits consistency when follow-up studies are performed by multiple
radiographers working different shifts. Regardless of which method is
employed to record this data, it is crucial that the information is
retrievable in some format. It is also crucial that radiographers review
this information prior to performing subsequent chest radiography.
The exposure for the AP portable chest radiograph should be made on
the second inspiration if possible. For patients who are unresponsive or
require mechanical ventilation by a respiratory therapist or
anesthesiologist, a coordinated effort will be necessary to ensure that
there is sufficient inspiration prior to making the exposure. Likewise,
if the patient is on a ventilator" ... carefully watch the
patient's chest to determine the inspiratory phase for the
exposure." (11)
Technical Evaluation Of a Chest Radiograph
Once the film has been exposed and processed, the responsibility of
reviewing it does not rest solely with the radiologist. The film first
should be evaluated by the radiographer. In a conversation with D.
Madden, M.D., (October 2006), he said "The technologist is
responsible for the technical excellence of the study." This
statement emphasizes the importance of obtaining a quality exam and
reinforces the fact that radiographers play an integral role in the care
of patients. A radiograph cannot be interpreted adequately by the
radiologist unless it is technically adequate.
The following considerations should be evaluated by the
radiographer prior to submitting the radiograph for review:
* Correct demographic information.
* Correct marker placement.
* Correct exposure.
* Adequate position.
* Sufficient inspiration.
* Pertinent anatomy demonstrated.
Correct Demographic Information
This information should include the patient's name and any
other identifying information deemed necessary by the institution. The
ACR guidelines suggest that each image be permanently marked with the
patient's name, the x-ray number or some other identifying number,
the date and time the exam was performed and the patient's date of
birth. (5)
Correct Marker Placement
The correct anatomical side marker, right or left, should be
visible on the final radiograph. Care should be exercised by the
radiographer to ensure that the marker will not interfere with
interpretation by covering pertinent anatomy. Additional care should be
exercised to make sure that the marker is placed on the correct side.
Conditions such as situs inversus show the importance of correct marker
placement. Situs inversus is a reversal of anatomy. As Wilhelm
explained: "In situs inversus, the morphologic right atrium is on
the left and the morphologic left atrium is on the right. The normal
pulmonary anatomy is reversed so that the left lung has 3 lobes and the
right 2 lobes. In addition, the liver and gallbladder are located on the
left, while the spleen and stomach are located on the right. The
remaining structures also are a mirror image of the normal." (15)
Markers are often color coded, which helps to reduce errors.
Nonetheless, radiographers always should check prior to making an
exposure to ensure that the correct marker is placed on the correct